<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    *{
      margin: 0;
      padding: 0;
    }
    div{
      position: absolute;
      width:200px;
      height: 200px;
    }
    .box1{
      background-color: #ff8500;

      z-index:1;
    }
    .box2{
      background-color: #03c8d4;
      top:60px;
      left:60px;

      z-index: 10;

    }
    .box3{
      background-color: darkred;
      top:120px;
      left:120px;
        /*可以与绝对定位一起做成背景*/
      /* position: absolute;*/
      z-index:-1;
    }
  </style>
</head>
<body>

<div class="box1">1</div>
<div class="box2">2</div>
<div class="box3">3</div>
</body>
</html>